Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: removing partition walls:

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Older houses were not built using the conventional framing provision of the
Code since the present code was not in existence at the time the house was
built. What we probably have was a house built according to standards at the
time the house was built which is probably less restrictive that our current
UBC.

My point is that these old houses and even new houses nowadays have been and
are being built based on standards which was believed to be adequate. To a
certain extent, they appear to be adequate, since there had been no major
failure of wood framed houses conventionally built. At least nothing that
required a major revision of the code(such as removal of the Conventional
Fraimng Provisions) or an additional provision in the code to correct a major
oversight or flaw. Except maybe for the rampant failure of cripple walls in
shear at raised floor houses after the Northridge Earthquake.

Personally, when I design a wood framed house for lateral loads, I have a
minimum standard. I require full shear transfer using shear blocking with
nails or A35 clips between the top of the interior shear wall and the roof
framing based on engineering calculations. If they want to build it based on
the UBC Conventional Framing Provision which does not require such connection,
I say "fine, but I'm not going to sign it. " My reason is I believe that
"engineered" buildings are the current standard practice in the industry.

However, that does not mean that "Unengineered Houses" or those built using
the UBC Conventinal Framing Provisions are not structural adequate. Maybe they
are. Or maybe they are just get overstressed during an earthquake but not
enough to cause failure. Maybe the "standard" during the the time these old
houses were built was that as long at the house does not collapse or suffer
major damage during an earthquake, it is "adequate".

This line of reasoning made me take a closer look at why these old
"unengineered houses" appear adequate, specifically, the issue of non-
engineered or no connection at the top interior wall to the roof framing. I
can see that at the worst case of the top of the wall hanging in the air with
no connection at all to any framing member, we still have the ceiling and wall
materials(lath and plaster, drywall, wood siding, etc) providing a full load
path for lateral loads to be transfered from the roof "assembly" to the
interior "shear" wall. This assumes that these materials are continuous(no
gaps or continuous open cracks) and are "adequately" connected together,
connected to the wall studs, top plates, and ceiling joists by nails, staples
or screws. Notice also that I said roof "assembly" because if nailed together
per standard or conventional framing provisions, the plywood sheathing is
nailed to the rafters, which is nailed to the top plate, in which the ceiling
joist is also nailed to, the whole thing is just one inteconnected piece.
Then, the lateral load from the roof assembly is transfered to the top plate
and is picked up by the ceiling joist which is picked up by the celing
material which is picked up by the wall material and transfered to the
interior wall.....and so on.......

My point is there is shear transfer, there is connection, and there is a
complete load path for lateral resistance. It is just "unengineered" or not
calculated due to its complexity and uncertainty. I think!!!

So, for my comment on the thread about removal of interior partition, I will
consider it an interior shear wall even if there is no top plate connection,
and replace it or compensate for its removal by some other means. Especially
if you are taking out a lot of interior walls.

Ernie Natividad